Senior German officials are seeking European support for a new global charter safeguarding personal privacy online, as the country's data protection watchdogs called for the suspension of a key agreement with the United States over revelations about US intelligence-gathering on the internet.

The moves reflect concerns in Germany that the US National Security Agency (NSA) may have collected personal information on millions of web users in breach of national and international rules. The claim, made by the NSA leaker Edward Snowden, has become an election issue in Germany two months before the country goes to the polls.

A letter sent by Germany's foreign and justice ministers to their European Union counterparts proposes expanding a 1966 UN human rights treaty to cover modern forms of communication such as email, instant messaging and social media.

"We want to use the current debate to launch an initiative that would outline the inalienable privacy rights under current conditions," the two ministers wrote. The letter, sent last week but released only on Wednesday, suggests convening a meeting of all 167 parties to the international covenant on civil and political rights. The United States ratified the treaty in 1992.

US officials have defended the NSA programmes as necessary to prevent terrorist attacks.

The 2000 "safe harbour" agreement requires US companies to grant European customers the same level of data protection they could expect in Europe – even if their data is processed or stored elsewhere. But according to Snowden, one NSA programme known as Prism gives the agency comprehensive access to customer data from companies such as Google and Facebook.

The data protection commissioners said the practice in effect made interception of personal data routine, rather than the exception, and urged European officials to consider suspending the agreement "in view of the excessive surveillance activities of foreign intelligence agencies".